Let me explain this as a casino dealer working in VIP salon.
When player doing 'rolling' , when means he will change all his commition chips to none-negotiable chips. And 'rolling turn over' is the total how much the player changed.
In my working casino, non-neg chips have to be lost and whatever the player won during the game will be paid by commition chips. So in the end the player will have commition chips instead of his original buyin non-neg chips. Then he does the rolling and cage ppl will record how much he commition chips he changed and give back him the equal value non-neg chips to start again. Casino will give about 0.6% rebat for the total turnover depends on the casino. The rate is different for each casino to each player.